A ketogenic amino acid is an amino acid that can be degraded directly into acetyl-CoA, which is the precursor of ketone bodies. This is in contrast to the glucogenic amino acids, which are converted into glucose. Ketogenic amino acids are unable to be converted to glucose as both carbon atoms in the ketone body are ultimately degraded to carbon dioxide in the citric acid cycle.
In humans, two amino acids are exclusively ketogenic: the “L” amino acids, Leucine and Lysine
In humans, five amino acids are both ketogenic and glucogenic: (ie, useful mnemonic “PITTT” or “FITTT”, and includes all the aromatic amino acids) Phenylalanine (abbreviated Phe or F, in contrast to Proline which is Pro or P, based on their respective pronunciations) Isoleucine, Threonine (some authors don’t recognize it as a ketogenic amino acid) Tryptophan, Tyrosine
In humans, the remaining thirteen amino acids are exclusively glucogenic (i.e. are not ketogenic).